str = "Always be careful"
import string
print str.replace("a", "b")
print str.replace("b", "a")
print str.replace("c", "&")

#decode the message
str = "Blwbys be cbreful"
print str.replace("a","b")
str = "Always ae careful"
print str.replace("b","a")
str = "Always be &areful"
print str.replace ("c","&")